1. Field of the Invention
Aspects of the present invention generally relate to a sheet feeding apparatus and an image forming apparatus equipped with the sheet feeding apparatus.
2. Description of the Related Art
Conventionally, an image forming apparatus for forming an image on a sheet is provided with a sheet feeding apparatus configured to elevate a stacking plate with sheets stacked thereon to bring the uppermost sheet into contact with a feeding roller to feed the sheet. In a sheet feeding apparatus as described above, each time a feeding operation is performed, the stacking plate is elevated by a cam configured to rotate with the feeding roller to move the sheets stacked on the stacking plate between positions where the feeding roller is urged to and separated from the sheets.
In such a construction, there is a difference in the timing with which the sheet contacts the feeding roller between the case when a full number of sheets are stacked on the stacking plate and the case when a small number of sheets are stacked thereon (hereinafter, referred to as the “small-number stacking”), resulting in variation in the interval between the sheets being fed. This is because, depending on the number of sheets stacked, there is a difference in the distance between the uppermost one of the sheets stacked on the stacking plate and the feeding roller when the cam lowers the stacking plate. Then, the smaller the number of sheets stacked on the stacking plate, the larger the distance between the uppermost sheet and the feeding roller, and the later the timing at which the sheet contacts the feeding roller, resulting in an increase in the interval between the sheets being fed.
In this connection, Japanese Patent No. 4312697 discusses a sheet feeding apparatus having a feeding roller provided with a low friction coefficient portion causing no feeding even if a sheet contacts the same to reduce variation between the sheets being fed.
However, in the sheet feeding apparatus discussed in Japanese Patent No. 4312697, it is necessary to provide both a low friction coefficient portion causing no sheet feeding to the feeding roller and a high friction coefficient portion causing sheet feeding thereto, so that the outer diameter of the feeding roller is required to be large. Then, when the outer diameter of the feeding roller increases, the size of the sheet feeding apparatus also increases.